The finely laminated sediment record of a permanent, hypersaline, desert oasis lake in the Ounianga region of northeastern Chad presents a unique opportunity to document the hydrological evolution of this groundwater-fed aquatic ecosystem during mid- and late-Holocene desiccation of the Sahara. In this study we reconstruct long-term changes in zoobenthos and zooplankton communities of Lake Yoa as their early-Holocene freshwater habitat changed into the hypersaline conditions prevailing today. Chironomid...

The Lake Yoa record and archaeological data provide adequate evidence that mid-Holocene
aridification did not occur abruptly across all of North Africa. Modeling results on the
issue of abrupt versus gradual desiccation of the Sahara are sufficiently diverse that paleoecological
data from a continuous natural archive can usefully guide the evaluation of model parameters
responsible for this diversity.

Large bodies of water in the middle of the desert are not only a natural spectacle, they also contain extremely precise environmental archives. Sediments extracted from these lakes document climate evolution and provide information on dust storms, savannah fires and volcanic eruptions.
A journey to north-east Chad
By Stefan Kröpelin

The fresh and saline lakes of Ounianga Kebir and Serir in northeastern Chad are among the very few permanent aquatic
ecosystems currently existing in the hyper-arid core of the Sahara desert. The confirmed modern fauna of aquatic molluscs at
Ounianga comprises three widespread species (Melanoides tuberculata, Biomphalaria pfeifferi and Lymnaea natalensis), of which
only the first appears to maintain a thriving population. We recovered seven more species of gastropods, among which one is new to
science...

Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural
archives recording its transition from a “green Sahara” to the present hyperarid desert. Our
continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive
drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the
African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled
by site-specific thresholds. Strong reductions...